Note the test files are not good tests, there were used to structure
development but do not adequately assert anything.

The plugins keeps a cache of ETags so we don’t need to access the store
to do validation.

This operates as a two tiered piece of middleware.

On the request side it checks if the request is a GET and if it includes
an If-None-Match header. If it does it looks up the current URI in the
cache and compares the value with what’s in the If-Match header. If they
are the same we can raise a 304 right now.

On the response side, if the current request is a GET and the outgoing
response has an ETag, put the current URI and ETag into the cache.

Store HOOKs are used to invalidate the cache through the management of
namespaces.

Installation is simply adding the plugin name to system_plugins and
twanager_plugins in tiddlywebconfig.py